Department of Molecular Chemistry & Biochemistry, Faculty of Science & Engineering, Doshisha University, Kyotanabe, Kyoto, 610-0321, Japan.
Macromol Rapid Commun. 2020 Apr;41(7):e1900650. doi: 10.1002/marc.201900650. Epub 2020 Feb 20.
Herein, the formation of unique shape-memory hydrogels that are composed of thermo-responsive amino-acid-derived vinyl polymer networks is reported; these are readily prepared by radical copolymerization of N-acryloyl glycinamide with commercially available cross-linkers, namely, methylenebis(acrylamide) and poly(ethylene glycol) diacrylate. These hydrogels are transparent (>90% transmittance at 600 nm) and are comprised of 97-70 wt% water. Furthermore, these contain both chemical and physical cross-linkages that are based on the multiple hydrogen bonds attained via amino acid units; this composition is aimed at generating opposing stimuli-responsive characters, namely, chemically stable and thermo-sensitive properties. A cooperative interplay of these two networks enables the hydrogels to exhibit a decent mechanical toughness (breaking strength ≈0.3 MPa and breaking elongation >600%) and a shape fix/memory capability. The temporary shape is easily fixed by cooling at 4 °C after deformation at high temperature, and it instantly recovers its original shape through reheating. Furthermore, a multi-shape memory effect is achieved by incorporating the pH-responsive N-acryloyl alanine unit into the hydrogel system as a comonomer; in this system, three distinct shapes can be fixed through temperature and pH manipulations. This facilely attainable shape memory hydrogel has significant potential in various fields, such as soft actuators, sensors, and biomedical materials.
本文报道了一种独特形状记忆水凝胶的形成，该水凝胶由热响应型氨基酸衍生的乙烯基聚合物网络组成；这些水凝胶可通过 N-丙烯酰甘氨酸酰胺与市售的交联剂，即亚甲基双（丙烯酰胺）和聚（乙二醇）二丙烯酸酯的自由基共聚很容易地制备。这些水凝胶是透明的（在 600nm 处>90%透光率），并且包含 97-70wt%的水。此外，这些水凝胶中既有基于氨基酸单元形成的氢键的化学交联，也有物理交联，这种组成旨在产生相反的刺激响应特性，即化学稳定性和热敏性。这两个网络的协同作用使水凝胶具有良好的机械韧性（断裂强度≈0.3MPa，断裂伸长率>600%）和形状固定/记忆能力。临时形状可以通过在高温下变形后冷却至 4°C 来轻松固定，并且通过重新加热可以立即恢复其原始形状。此外，通过将 pH 响应性 N-丙烯酰丙氨酸单元作为共聚单体引入水凝胶体系中，可以实现多形状记忆效应；在该体系中，可以通过温度和 pH 控制来固定三种不同的形状。这种易于获得的形状记忆水凝胶在软驱动器、传感器和生物医学材料等各个领域具有重要的应用潜力。
